This section is intended to introduce the reader to various aspects of the art that may be related to various aspects of the present invention. The following discussion is intended to provide information to facilitate a better understanding of the present invention. Accordingly, it should be understood that statements in the following discussion are to be read in this light, and not as admissions of prior art.
Ethylene is used as the building block for the production of polyethylene, glycol, polyester, and styrene monomer. Global production of ethylene from olefin plants has reached over 150 million metric-tons in 2012, according to Gulf Petrochemicals and Chemicals Association, making ethylene one of the largest produced chemical commodities, by volume, in existence today.
Production of ethylene is achieved by cracking a gaseous or liquid hydrocarbon feedstock, such as ethane, propane, naphtha, or gas oil in the presence of steam inside the coils of a pyrolysis furnace. Hydrocarbon cracking is accomplished at low pressures (up to a few atmospheres) and elevated temperatures in the range of 750-1150° C. The feedstock is passed at high velocities through heated coils which are made from superalloys primarily comprised of iron, nickel and chromium. The hydrocarbon cracking time, or residence time, within the coils is extremely short, generally less than a fraction of a second.
These pyrolysis furnace coils are subjected to some of the most severe operating conditions in the petrochemical industry, experiencing extreme thermal cycling, coking, carburization, oxidation and creep during service, resulting in reduced service life and frequent premature pipe failures. This family of iron, nickel and chromium superalloys may well have reached their ultimate operating limits as the past few decades have seen a trend of increasing furnace temperature in efforts to increase yield and efficiency from the endothermic cracking process. Furthermore, this metal superalloy combination in general has always been hindered by temperature limits and the frequent maintenance required for coke removal. The main objective of this invention is to provide an alternative path to achieve coils operating at higher temperature with reduced coking, thus increasing the production capabilities of ethylene furnaces. This alternative path described here will be through the use primarily of silicon carbide.